44 U.S. Code § 1123 - Binding materials; bookbinding for libraries

Binding for the departments of the Government shall be done in plain sheep or cloth, except that record and account books may be bound in Russia leather, sheep fleshers, and skivers, when authorized by the head of a department. The libraries of the several departments, the Library of Congress, the libraries of the Surgeon General’s Office, and the Naval Observatory may have books for the exclusive use of these libraries bound in half Turkey, or material no more expensive.